In a synchronous digital communication or broadcasting system, owing to the influence of Doppler Frequency offset and the local carrier error, the frequency of the received signal will be shifted. The frequency offset will cause an additional phase rotation of the received signal which will seriously deteriorate the performance of the receiver.
Especially in multi-carrier modulation technology as used in an Orthogonal Frequency Division Multiplexing (OFDM) transmission system which splits a high-rate data-stream into a number of lower rate streams to be transmitted simultaneously over a number of sub-carriers, a carrier frequency offset will introduce Inter-Carrier Interference (ICI) reducing the orthogonality of the sub-carriers. Therefore, the OFDM systems are very sensitive to Carrier frequency offset. The problem is important for the consumer perceived quality in a consumer-oriented receiver based on OFDM technology.
As for frequency offset estimation in a traditional OFDM system based on Digital Terrestrial Media Broadcasting Standards, it will usually include two parts: an integer frequency offset (IFO, multiple of subcarrier interval) and a fraction frequency offset (FFO, less than half of subcarrier interval). The IFO can be determined through cross correlation using pilots in the frequency domain, while the FFO can be determined through auto correlation using cyclic prefixes in time domain.